It is oftentimes desired that the size and/or velocity of small particles be measured and devices have been heretofore suggested and/or utilized to accomplish this end. It has been heretofore found, for example, that small particles can be measured by directing the particles through a laser beam and determining particle size by collecting light scattered by the beam (see, for example, U.S. Pat. No. 3,406,289).
While such measurements have been found to be useful for detecting particle size, such systems have generally heretofore required that the particles be directed through the center of the laser beam where the intensity is the greatest and can be considered to be uniform.
It has also been heretofore suggested that a laser beam could be split and the resulting beams thereafter utilized, and such split beams have been used heretofore, for example, to compare optical path lengths in a multiple laser beam fusion system (see U.S. Pat. No. 4,272,193). In addition, laser beams have heretofore been combined and the combined beam utilized to evaluate cell volume, for example, by providing fluorescence volume exclusion signals (see U.S. Pat. No. 4,284,355).